(a) FIELD OF THE INVENTION
The present invention relates to an electronic endoscope which uses a solid-state image pickup device.
(b) DESCRIPTION OF THE PRIOR ART
A solid-state image pickup device, in general, is sensitive to infrared rays, so that it is necessary for an electronic endoscope which uses, a solid-state image pickup device to have an infrared ray removing filter incorporated in its optical system. In the past, there has been known an electronic endoscope having such a structure as shown in FIG. 1. That is, in FIG. 1, reference numeral 1 denotes the body of an electronic endoscope; 2 a light supply; 3 an infrared ray removing filter; 4 a collector lens; 5 a light guide made of a bundle of optical fibers and housed in the body 1; 6 an illuminating lens housed in the forward end portion of the body 1; 7 an objective lens housed in the distal end portion of the body 1; 8 a solid-state image pickup device such as CCD housed in the forward end portion of the body 1; 9 a control unit inputted with a signal delivered from the solid-state image pickup device 8; and 10 a TV monitor. According to the electronic endoscope having such an arrangement as mentioned above, the beam of light emitting from the light supply 2 is removed of its infrared ray component by the infrared ray removing filter 3 and thereafter the resulting beam of light passes through the light supply lens 4 and through the light guide 5 and illuminates an object S through the illuminating lens 6. The light reflected from the object S which is thus illuminated is focused, by the objective lens 7, on the solid-state image pickup device 8, and the focused image is displayed on the TV monitor 10 by the control unit 9. In such a case, the beam of light which is incident to the solid state image pickup device 8 has been removed of its infrared ray component by the infrared ray removing filter 3, so that an appropriate image of the object can be displayed on the TV monitor 10. In this arrangement of the endoscope, however, the infrared ray removing filter 3 is disposed in the path of an intensive light supply, and accordingly there has been the inconvenience that the filter would crack as it is subjected to the heat produced by the beam of light coming from the light supply. Also, in case an irradiation of, for example, a laser beam is performed by means of a YAG laser 12 with a laser probe 11 made of a single optical fiber and passed through a forceps channel formed in the body 1 of the electronic endoscope, the laser beam thus produced is an infrared beam of light having a wavelength of 1061 nm. Therefore, the solid-state image pickup device 8 senses this laser beam, and as a result the observation is disturbed.